The invention relates generally to immunoconjugates for diagnostic and therapeutic uses in cancer. In particular, the invention relates to recombinantly produced chimeric and humanized monoclonal antibodies directed against B-cell lymphoma and leukemia cells, which antibodies can be covalently conjugated to a diagnostic or therapeutic reagent without loss of antibody binding and internalization function and with reduced production of human anti-mouse antibodies.
Non-Hodgkins lymphoma (NHL) and chronic lymphocytic leukemia are B-cell malignancies that remain important contributors to cancer mortality. The response of these malignancies to various forms of treatment is mixed. They respond reasonably well to chemotherapy, and, in cases where adequate clinical staging of NHL is possible, as for patients with localized disease, satisfactory treatment may be provided using field radiation therapy (Hall et al., Radiology for the Radiologist, Lippincott, Philadelphia, 1989, pp 365-376). However, the toxic side effects associated with chemotherapy and the toxicity to the hematopoietic system from local, as well as whole body, radiotherapy, limits the use of these therapeutic methods. About one-half of the patients die from the disease (Posner et al., Blood, 61: 705 (1983)).
The use of targeting monoclonal antibodies conjugated to radionuclides or other cytotoxic agents offers the possibility of delivering such agents directly to the tumor site, thereby limiting the exposure of normal tissues to toxic agents (Goldenberg, Semin. Nucl. Med., 19: 332 (1989)). In recent years, the potential of antibody-based therapy and its accuracy in the localization of tumor-associated antigens have been demonstrated both in the laboratory and clinical studies (see., e.g., Thorpe, TIBTECH, 11: 42 (1993); Goldenberg, Scientific American, Science & Medicine, 1: 64 (1994); Baldwin et al., U.S. Pat. No. 4,925,922 and 4,916,213; Young, U.S. Pat. No. 4,918,163; U.S. Pat. No. 5,204,095; Irie et al., U.S. Pat. No. 5,196,337; Hellstrom et al., U.S. Pat. Nos. 5,134,075 and 5,171,665). In general, the use of radio-labeled antibodies or antibody fragments against tumor-associated markers for localization of tumors has been more successful than for therapy, in part because antibody uptake by the tumor is generally low, ranging from only 0.01% to 0.001% of the total dose injected (Vaughan et al., Brit. J. Radiol., 60: 567 (1987)). Increasing the concentration of the radiolabel to increase the dosage to the tumor is counterproductive generally as this also increases exposure of healthy tissue to radioactivity.
LL-2 (EPB2) is a highly specific anti-B-cell lymphoma and anti-lymphocytic leukemia cell murine monoclonal antibody (mAb) that is rapidly internalized by such cells and that can overcome some of the aforementioned difficulties (Shih et al., Int. J. Cancer, 56: 538 (1994)). LL2, which is of the IgG2a antibody type, was developed using the Raji B-lymphoma cell line as the source of antigen (Pawlak-Byczkowska et al., Cancer Res., 49: 4568 (1989)). Murine LL2 (mLL2) is known to react with an epitope of CD22 (Belisle et al., Proc Amer. Assn. Clin. Res., 34: A2873 (1993)). CD22 molecules are expressed in the cytoplasm of progenitor and early pre-B cells, and appear in the cell surface of mature B-cells.
By immunostaining of tissue sections, mLL2 was shown to react with 50 of 51 B-cell lymphomas tested. mLL2 is a highly sensitive means of detecting B-cell lymphoma cell in vivo, as determined by a radioimmunodetection method (Murthy et al., Eur. J. Nucl. Med., 19: 394 (1992)). The Fab' fragment of mLL2 labeled with .sup.99m Tc localized to 63 of 65 known lesions in Phase II trial patients with B-cell lymphoma (Mills et al., Proc. Amer. Assn. Cancer Res., 14: A2857 (1993)). In addition, .sup.131 I-labeled mLL2 was therapeutically effective in B-cell lymphoma patients (Goldenberg et al., J. Clin. Oncol., 9: 548 (1991)). mLL2 Fab' conjugated to the exotoxin PE38KDEL induced complete remissions of measurable human lymphoma xenografts (CA-46) growing in nude mice (Kreitman et al., Cancer Res., 53: 819 (1993)).
The clinical use of mLL2, just as with most other promising murine antibodies, has been limited by the development in humans of a HAMA response. While a HAMA response is not invariably observed following injection of mLL2, in a significant number of cases patients developed HAMA following a single treatment with mLL2. This can limit the diagnostic and therapeutic usefulness of such antibody conjugates, not only because of the potential anaphylactic problem, but also as a major portion of the circulating conjugate may be complexed to and sequestered by the circulating anti-mouse antibodies. This is exemplified by one study in which about 30% of the patients developed low level HAMA response following a single injection of about 6 mg of mLL2 .sup.131 I-IgG and nearly all developed a strong HAMA response with additional injections. On the other hand, with mLL2 Fab' labeled with .sup.99m Tc, no HAMA response was observed. Such HAMA responses in general pose a potential obstacle to realizing the full diagnostic and therapeutic potential of the mLL2 antibody.
Although, as noted above, the use of fragments of mLL2, such as F(ab').sub.2 and Fab', partially alleviate/circumvent these problems of immunogenicity, there are circumstances in which whole IgG is more desirable, such as when induction of cellular immunity is intended for therapy, or where an antibody with enhanced survival time is required.
In order to maximize the value of the mLL2 IgG antibody as a therapeutic or diagnostic modality and increase its utility in multiple and continuous administration modalities, it is an object of this invention to produce a mouse/human chimeric mAb (cLL2) and a humanized mAb (hLL2) related to mLL2 that retain the antigen-binding specificity of mLL2, but that elicit reduced HAMA in a subject receiving same.
It is another object of this invention to provide DNA sequences encoding the amino acid sequences of the variable regions of the light and heavy chains of the cLL2 and hLL2 mabs, including the complementarity determining regions (CDR).
It is also an object of this invention provide conjugates of the hLL2 and cLL2 mAbs containing therapeutic or diagnostic modalities.
It is a further object of this invention to provide methods of therapy and diagnosis that utilize the humanized and chimeric mabs of the invention.
These objects have been achieved by the invention described below in the specification and appended claims.